Baculovirus Replication: Stimulation of Thymidine Kinase and DNA Polymerase Activities in Spodopterafrugiperda Cells Infected with Trichoplusia ni Nuclear Polyhedrosis Virus

Baculoviruses are large DNA-containing viruses which replicate in the nucleus of invertebrate cells. The viruses contain supercoiled DNA of tool. wt. about 8 x l 0 7 (Bud & Kelly, 1977) and the multiply enveloped nuclear polyhedrosis virus of Trichoplusia ni used in this study has a genome size of 8.3 x 107 (Bud & Kelly, 1980). Little is known about the replication of baculoviruses in molecular terms. The viruses sequentially induce 30 to 35 polypeptides in infected cells (Carstens et al., 1979); it has been suggested that at least four phases (named ~ fl, ~ and ~ from earliest to latest) of induction of polypeptides occur in a cascade fashion (Kelly & Lescott, 1980) typical of a number of large DNA viruses (Honess & Roizman, 1974; Elliott & Kelly, 1980). When baculovirus DNA replication is prevented, the induction of virus-specific polypeptides fails to progress beyond immediate early a or early/~ polypeptide synthesis (Kelly & Lescott, 1980). Virus DNA synthesis occurs from about 6 to 8 h after infection (Tjia et al., 1979; D. C. Kelly & M. D. Ayres, unpublished observations). In a previous paper, we have shown that a number of non-structural polypeptides (i.e. polypeptides not detected in virus particles or polyhedra) are induced in baculovirus-infected cells (Kelly & Lescott, 1980). This paper reports that thymidine kinase and DNA polymerase activities, candidate functions for non-structural polypeptides, are stimulated in baculovirusinfected cells. These two enzyme activities were investigated to provide markers for non-structural functions in future genetic studies of these viruses. The basic biochemical properties of these two activities are reported in this paper.